The present invention relates to a method and machine for grinding pregeared bevel gears.
Grinding machines for grinding bevel gears which have circularly shaped tooth flanks have been known. Such tooth surfaces of bevel gears have been ground with the aid of an elliptical additional movement imparted to the grinding head, as has been disclosed, for example in German patent publication No. P 29 45 483.9-14. Other tooth surface shapes have been also ground by the known machines. This elliptical additional movement is performed in a very quick operation which is important in mass production.
In other known methods of grinding tooth profiles of pregeared bevel gears two flanks of only disc-shaped gears have been ground in one setting of the grinding tool whereas for grinding bevel gears two different working operations have been required, or it has been necessary to employ grinding wheels with coatings for the wheel and the counterwheel unless a special construction of the bevel gear toothing required the grinding of both flanks of each tooth in one setting with the crown grinding wheel. This last method, however, strongly limits the possiblities of grinding of the toothing.
The present invention relates to a machine for grinding pregeared bevel gears in one setting at the right-hand and the left-hand flanks by a single tool.
Grinding machines of the aforementioned type have been proposed in, for example, Offenlegungsschrifts Nos. 2,721,164 and 2,945,483.
During the manufacturing of toothed bevel gears in a hobbing process, the workpiece is usually secured to the spindle of the workpiece carrier while the grinding wheel is received on the hob member of the tool carrier. The grinding wheel and the workpiece are applied to each other in the known hobbing motion by which the tooth shape in the direction of the tooth depth is generated. The grinding wheel defines the tooth shape in the direction of elongation of the tooth. The cutting motion of the grinding wheel causes a material removal in the known fashion. The eccentricity between the grinding spindle and the central axis of the machine causes a desired angle of the tooth. If a radial displacement "e" is imparted to the grinding wheel the above eccentricity is adjusted to that displacement in order to produce a combination of the tool radii and the angle of the tooth in the correct manner. The "radial" displacement can be varied for the right-hand flank and the left-hand flank of the tooth, whereby the displacements of the carrier from the inner end of the tooth to the outer end of the tooth and in the opposite direction can be made independent from each other. The hobbing movement as well as all secondary movements of the tool grinding wheel are numerically controlled so that a mechanical transmission for coordinating all these motions can be omitted. The balancing rotation required to produce a correct tooth gap, can be also provided by a numerical control of the machine. If the eccentricity is introduced in the multiple control of the machine the "radial" displacement of the grinding wheel can be executed with a high precision and in a very short period of time during the change from the forward hobbing to the backward hobbing.
Furthermore, the grinding tool, that is, a grinding wheel, and up the radial movement of the grinding tool may be moved toward the truing device and thereby a radius of the grinding wheel is determined.
By virtue of the "radial" displacement, the grinding wheel can be moved toward the truing roller so that the radius of the grinding wheel may be determined. Likewise the grinding wheel can be also moved toward the other side of the truing tool for an inner truing.
The truing device may be pivotable and an angle of engagement of the truing device with said grinding wheel is adjustable by a pivoting movement of said truing device.
The grinding wheel has a cutting front edge having a contour, with the contour being adjustable by a respective coordination between a depth infeed of the truing device and the radial movement of the grinding wheel. The depth infeed allows for a backward movement of the grinding wheel from the truing roller whereby the eccentricity can be increased when the grinding wheel is pulled somewhat back and then again moved toward the truing tool.
Upon the coordination of the depth infeed and the eccentricity the front edge of the grinding wheel can correspond to the contour of the front edge of, for example, a diamond truing roller so that a tooth base of the bevel gear is obtained.
The pivoting movement and the depth infeed of the truing device may be numerically controlled for generating a correct tooth foot contour.
In accordance with the present invention a grinding machine for grinding pregeared bevel gears is provided, with the grinding machine comprising a stationary machine bed, a workpiece carrier for a bevel gear, a motor driven spindle in the workpiece carrier and holding a bevel to be ground, a motor driven grinding head having a grinding spindle, a grinding wheel on the grinding spindle, and a truing device cooperating with the grinding wheel. The grinding wheel and the bevel gear being ground execute a hobbing motion to generate a shape of a tooth in a direction of the tooth depth, and the grinding wheel defines the shape of the tooth in a longitudinal direction of the tooth, with a cutting motion of a grinding wheel resulting in a metal removal from the pregeared bevel gear being ground. An eccentricity of the grinding spindle to a center of the grinding machine results in a desired angle of the tooth. The truing device is connected to a rigid part of the machine, and is pivotable relative to said grinding wheel for changing an angle of engagement with the grinding wheel. An individual motor is provided for independently driving the truing device, and the grinding head is adjustable by a motor in a radial direction to the bevel gear and also in a direction perpendicular to the radial direction over a limited distance.
By virtue of the features of the grinding machine of the present invention, it is possible to grind pregeared gears with epicycliodes, which, up to the present time, was not possible.
According to the present invention, the truing tool is mounted above the grinding machine on a special frame and, the truing device is rigidly connected to either the machine bed or to another rigid part of the machine, such as, for example a workpiece carrier.
The grinding machine according to the invention makes it possible to correct an angle of engagement of the truing tool with the grinding wheel due to the pivoting motion of the truing device. The truing roller is independently driven so that any coordination between the speed of the grinding wheel and that of the truing tool is possible.
In accordance with further features of the present invention, the truing device includes a truing roller having a central axis 5 with the grinding wheel having a peripheral line parallel to said central axis.
Advantageously, the grinding machine may further include a workpiece carriage and a tool carriage, with the carrier for a bevel gear being mounted on the workpiece carriage, and the grinding head mounted to the tool carriage. A profile of the grinding wheel without high cambering is produced by the truing device upon a linear superposition of a depth infeed of the workpiece carriage and an eccentricity adjustment, e.g. "radial" displacement of the tool carriage.
The truing tool may have a center point for a radius for cambering the grinding wheel, and a high cambering of the grinding wheel is produced when a linear coordination of a depth infeed and the adjustment of said tool carriage is provided, and then a cambering motion of the truing tool is so overlapped that the center point of said radius executes such a curved motion that a desired cambering is brought onto said grinding wheel. The truing tool may be a roller, or an individual diamond or a diamond roller with the straight line flank profile. For example, a corund grinding wheel can be profiled with the aid of the silicon carbide grinding disc. With the aid of the grinding machine of the invention the truing of Borazon in the grinding machine is possible. If the grinding wheel is to be profiled with the diamond roller or the grinding disc, it is expedient that the truing device be pivoted by the pivoting device in accordance with an engagement angle difference between the inner and outer angle of the cutting edge of the grinding wheel. The truing device can be rigidly mounted when, for example the axis of the truing tool extends parallel to the axis of the grinding wheel and a necessary correction is made via the NC-machine control.
The above and additional objects, features, and advantages of the present invention will become more apparent from the following description when taken in connection with the accompanying drawings which show, for the purposes of illustration only, several embodiments in accordance with the present invention.